Conventionally, as shown in FIG. 14, a vehicle seat frame is known, which includes a seat cushion frame 110 supporting a seat cushion 90, a seat back frame 120 supporting a seat back 91, a recliner 140 rotatably connecting the seat back 91 relative to the seat cushion 90 and adjusting the rotation angle thereof and a shoulder belt anchor 130 provided at an upper end of the seat back frame 120. (For example, a vehicle seat frame disclosed in the Patent Document 1). Back side frames 121 and 122 are provided at both sides of the seat back frame 120 and a hollow square prism shaped back center frame 113 is provided at the central portion thereof. Further, cushion side frames 111 and 112 are provided at both sides of the seat cushion frame 110 and a cushion center frame 113 is provided at the central portion thereof. An upper arm 124 formed with a plank is connected to the under portion of the back center frame 113 through bolt means and a lower arm 114 formed with a plank is connected to the upper portion of the back center frame 113 through bolt means. The recliner 140 is provided between the upper arm 124 and lower arm 114. The recliner 140 rotatably connects the upper and lower arms 124 and 114.
Further, a retractor 150 is attached to the seat back frame 120 and one end of a seat belt 151, which is structured with a shoulder belt portion 151a and a lap belt portion 151b, is retracted into the retractor 150. The other end of the seat belt 151 is fixed to an anchor plate 115 attached to the cushion center frame 113 and the middle portion of the seat belt 151 is inserted into a tongue plate 152. This tongue plate 152 is detachably attached to a buckle 116 attached to the cushion side frame 111. It is noted that the vehicle seat frame is a seat frame for two occupants and an explanation of the other seat belt for the other person is omitted.
According to this vehicle seat frame, the seat belt 151 is locked to secure the safety of an occupant seated thereon when the vehicle is suddenly decelerated.    Patent Document 1: JA 2002-59770 A